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Fundamentals and Applications of Magnetic Materials$
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Kannan M. Krishnan

Print publication date: 2016

Print ISBN-13: 9780199570447

Published to Oxford Scholarship Online: December 2016

DOI: 10.1093/acprof:oso/9780199570447.001.0001

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Magnetic Information Storage

Magnetic Information Storage

(p.716) 14 Magnetic Information Storage
Fundamentals and Applications of Magnetic Materials

Kannan M. Krishnan

Oxford University Press

Magnetic information storage has evolved rapidly, with advances in materials, either by scaling or by incorporating newly discovered phenomena, contributing significantly in their evolution from tapes, to HDDs in both longitudinal and perpendicular geometries, to solid-state memory devices. This chapter presents a comprehensive overview, covering in detail the principles of the recording process and a qualitative description of current and emerging technologies. In general, the width of a recorded transition is proportional to the magnetization–thickness product (Mrδ) of the medium; this should be as small as possible. Noise in the recorded signal is dominated by the physical microstructure of the medium and high recording densities require smallest grain sizes (Dg). There are two time scales of interest in recording: short (10−9 s), governed by the switching of the medium within the short write pulse, and long (~10 years), defined by the required stability of the recorded information for subsequent retrieval. The trade-offs between three competing requirements to achieve high signal to noise, long-term thermal stability of the written bits, and writeability within the limits of maximally generated write fields, provide an ongoing challenge in HDD media design and development. Different approaches to increasing areal densities in magnetic recording are presented, with heat-assisted magnetic recording (HAMR) and bit-patterned media (BPM) currently being favored; in addition, solid-state magnetic memory architectures, such as STT-MRAM and devices using current-induced domain wall motion, appear promising.

Keywords:   principles of magnetic recording, transition width, noise sources, longitudinal and perpendicular recording, HAMR, bit-patterned media, STT-MRAM, non-volatile memory

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